The manufacture of plastic bags from a flattened, tubular web movable in a production direction with a machine having input rollers, output rollers, a cutting device and a transverse bag welding device is known.
The cutting device can produce a wavelike cut in the flattened, tubular web running in the web-feed direction. This wavelike cut can define two halves or web sections which have complementary upper hand grips.
Between the cutting device and the transverse bag-welding device a detour device is positioned which causes a phase shift in the web sections with respect to the wavelike cut when one of the web sections is passed through the detour device.
The detour apparatus thus positions the bag hand grips over one another. The phase-shifted web sections are jointly fed into the transverse bag-welding apparatus to close the sides of the plastic bags. The cutting apparatus has a knife as well as a knife control roller with a cutting knife groove therein and the cutting knife is held in a cutting groove over which the flattened, tubular strip is fed.
In such an apparatus, e.g. as described in German Patent DE-OS No. 30 04 220, corresponding to U.S. Pat. No. 4,398,903, the flattened tubular web is fed over a roller which extends across the entire width of the tubular web.
The web is typically synchronized with the roller systems and bears a cut or incision which when examined appears more or less sinusoidal. The rollers flank the tubular web.
The cutting knife control roller is constructed to come near those rollers, carries the knife control groove and holds a conforming structure in the knife groove.
The cutting knife control groove and the knife cutting groove are formed with great precision so that on operation the cut previously mentioned is satisfactory and is free from chatter marks and the like. To allow the stacking of the manufactured plastic bags, the feed of the strip may be temporarily interrupted by frequent unavoidable idle periods so that a basic inertia problem arises on renewed running.
It is thus possible that the cut in the strip will not be uniform with renewed running but will show an almost continuous set of faults.